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MnTe has recently attracted attention as an altermagnetic candidate. Experimentally it has an altermagnetic order of ferromagnetic $ab$ planes, stacked antiferromagnetically along $c$. We show that this magnetic order (by itself non-trivial, since the in-plane exchange in antiferromagnetic) opens intriguing possibility of manufacturing altermagnetically-detwinned samples and generate observable magnetooptical response (which we calculate from first principles) as a signature of altermagnetism., Comment: One reference is corrected

Ising superconductivity, observed experimentally in NbSe$_{2}$ and similar materials, has generated tremendous interest. Recently, attention was called to the possible role that spin fluctuations (SF) play in this phenomenon, in addition to the dominant electron-phonon coupling (EPC); the possibility of a predominantly-triplet state was discussed and led to a conjecture of viable singlet-triplet Leggett oscillations. However, these hypotheses have not been put to a quantitative test. In this paper, we report first principle calculations of the EPC and also estimate coupling with SF, including full momentum dependence. We find that: (1) EPC is strongly anisotropic, largely coming from the K-K' scattering, and therefore excludes triplet symmetry even as an excited state; (2) superconductivity is substantially weakened by SF, but anisotropy remains as above; and, (3) we do find the possibility of a Leggett mode, not in a singlet-triplet but in an $s_{++}$ - $s_\pm$ channel., Comment: 11 pages, 4 figures

When sulfur and silicon are incorporated in monolayer 2H-NbSe

Identification, understanding, and manipulation of novel magnetic textures are essential for the discovery of new quantum materials for future spin-based electronic devices. In particular, materials that manifest a large response to external stimuli such as a magnetic field are subject to intense investigation. Here, we study the kagome-net magnet YMn

Recent observations [A. Pustogow et al., Nature (London) 574, 72 (2019).NATUAS0028-083610.1038/s41586-019-1596-2] of a drop of the ^{17}O nuclear magnetic resonance (NMR) Knight shift in the superconducting state of Sr_{2}RuO_{4} challenged the popular picture of a chiral odd-parity paired state in this compound. Here we use polarized neutron scattering (PNS) to show that there is a 34±6% drop in the magnetic susceptibility at the Ru site below the superconducting transition temperature. We measure at lower fields H∼1/3H_{c2} than a previous PNS study allowing the suppression to be observed. The PNS measurements show a smaller susceptibility suppression than NMR measurements performed at similar field and temperature. Our results rule out the chiral odd-parity d=z[over ^](k_{x}±ik_{y}) state and are consistent with several recent proposals for the order parameter including even-parity B_{1g} and odd-parity helical states.

The recently discovered Fe-based superconductor (FeBS) LaFe_{2}As_{2} seems to break away from an established pattern that doping an FeBS beyond 0.2e/Fe destroys superconductivity. LaFe_{2}As_{2} has an apparent doping of 0.5e, yet superconducts at 12.1 K. Its Fermi surface bears no visual resemblance with the canonical FeBS fermiology. It also exhibits two phases, none magnetic and only one superconducting. We show that the difference between them nonetheless has a magnetic origin, the one featuring disordered moments, and the other locally nonmagnetic. We find that La there assumes an unusual valence of +2.6 to +2.7, so that the effective doping is reduced to 0.30-0.35e. A closer look reveals the same key elements: hole Fermi surfaces near Γ-Z and electron ones near the X-P lines, with the corresponding peak in susceptibility, and a strong tendency to stripe magnetism. The physics of LaFe_{2}As_{2} is thus more similar to the FeBS paradigm than hitherto appreciated.

We present a combined experimental and theoretical study of the mineral atacamite Cu_{2}Cl(OH)_{3}. Density-functional theory yields a Hamiltonian describing anisotropic sawtooth chains with weak 3D connections. Experimentally, we fully characterize the antiferromagnetically ordered state. Magnetic order shows a complex evolution with the magnetic field, while, starting at 31.5 T, we observe a plateaulike magnetization at about M_{sat}/2. Based on complementary theoretical approaches, we show that the latter is unrelated to the known magnetization plateau of a sawtooth chain. Instead, we provide evidence that the magnetization process in atacamite is a field-driven canting of a 3D network of weakly coupled sawtooth chains that form giant moments.

Triplet pairing in Sr_{2}RuO_{4} was initially suggested based on the hypothesis of strong ferromagnetic spin fluctuations. Using polarized inelastic neutron scattering, we accurately determine the full spectrum of spin fluctuations in Sr_{2}RuO_{4}. Besides the well-studied incommensurate magnetic fluctuations, we do find a sizable quasiferromagnetic signal, quantitatively consistent with all macroscopic and microscopic probes. We use this result to address the possibility of magnetically driven triplet superconductivity in Sr_{2}RuO_{4}. We conclude that, even though the quasiferromagnetic signal is stronger and sharper than previously anticipated, spin fluctuations alone are not enough to generate a triplet state strengthening the need for additional interactions or an alternative pairing scenario.

Dilute magnetic semiconductors (DMS) are nonmagnetic semiconductors doped with magnetic transition metals. The recently discovered DMS material (Ba$_{1-x}$K$_{x}$)(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ offers a unique and versatile control of the Curie temperature, $T_{\mathrm{C}}$, by decoupling the spin (Mn$^{2+}$, $S=5/2$) and charge (K$^{+}$) doping in different crystallographic layers. In an attempt to describe from first-principles calculations the role of hole doping in stabilizing ferromagnetic order, it was recently suggested that the antiferromagnetic exchange coupling $J$ between the nearest-neighbor Mn ions would experience a nearly twofold suppression upon doping 20\% of holes by potassium substitution. At the same time, further-neighbor interactions become increasingly ferromagnetic upon doping, leading to a rapid increase of $T_{\mathrm{C}}$. Using inelastic neutron scattering, we have observed a localized magnetic excitation at about 13 meV, associated with the destruction of the nearest-neighbor Mn-Mn singlet ground state. Hole doping results in a notable broadening of this peak, evidencing significant particle-hole damping, but with only a minor change in the peak position. We argue that this unexpected result can be explained by a combined effect of superexchange and double-exchange interactions.

While the phase diagrams of the one- and multiorbital Hubbard model have been well studied, the physics of real Mott insulators is often much richer, material dependent, and poorly understood. In the prototype Mott insulator V_{2}O_{3}, chemical pressure was initially believed to explain why the paramagnetic-metal to antiferromagnetic-insulator transition temperature is lowered by Ti doping while Cr doping strengthens correlations, eventually rendering the high-temperature phase paramagnetic insulating. However, this scenario has been recently shown both experimentally and theoretically to be untenable. Based on full structural optimization, we demonstrate via the charge self-consistent combination of density functional theory and dynamical mean-field theory that changes in the V_{2}O_{3} phase diagram are driven by defect-induced local symmetry breakings resulting from dramatically different couplings of Cr and Ti dopants to the host system. This finding emphasizes the high sensitivity of the Mott metal-insulator transition to the local environment and the importance of accurately accounting for the one-electron Hamiltonian, since correlations crucially respond to it.

The heterointerfacing of different materials with competing magnetic orders forms the basis for today’s spintronic devices, however materials compatibility has remained a major limitation to the conception of new multilayered systems. Here, we uncover a multilayer of competing magnetic orders within a single layer of FeRh after low-energy He-ion irradiation: metamagnetic, ferromagnetic, and spin glass. Polarized neutron reflectometry, irradiation modeling, and density functional theory calculations reveal a direct correlation between the disorder concentration, the depth-dependent magnetic ordering, and the onset of the metamagnetic transition. Such a heterostructure opens the door to new paradigms in antiferromagnetic electronics and ultra-low-power magnetization controllability. IMPACT STATEMENT This unlocks the possible use of intrinsic magnetism as a state-variable for logical computation via a top-down approach to the multilayering/control of magnetic order in a single metamagnetic thin film.

A tendency to form benzene-like molecular orbitals has been recently shown to be a common feature of the $4d$ and $5d$ transition metal oxides with a honeycomb lattice. This tendency competes with other interactions such as the spin-orbit coupling and Hubbard correlations, and can be partially or completely suppressed. In the calculations, SrRu$_{2}$O$_{6}$ presents the cleanest, so far, case of well-formed molecular orbitals, however, direct experimental evidence for or against this proposition has been missing. In this paper, we show that combined photoemission and optical studies can be used to identify molecular orbitals in SrRu$_{2}$O$_{6}$. Symmetry-driven election selection rules suppress optical transitions between certain molecular orbitals, while photoemission and inverse photoemission measurements are insensitive to them. Comparing the photoemission and optical conductivity spectra one should be able to observe clear signatures of molecular orbitals.

We report a combination of Fe K$\beta$ x-ray emission spectroscopy and $ab$-intio calculations to investigate the correlation between structural and magnetic degrees of freedom in CaFe$_{2}$(As$_{1-x}$P$_{x} $)$_{2}$. The puzzling temperature behavior of the local moment found in rare earth-doped CaFe$_{2}$As$_{2}$ [\textit{H. Gretarsson, et al., Phys. Rev. Lett. {\bf 110}, 047003 (2013)}] is also observed in CaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$. We explain this phenomenon based on first-principles calculations with scaled magnetic interaction. One scaling parameter is sufficient to describe quantitatively the magnetic moments in both CaFe$_{2}$(As$_{1-x}$P$_{x} $)$_{2}$ ($x=0.055$) and Ca$_{0.78}% $La$_{0.22}$Fe$_{2}$As$_{2}$ at all temperatures. The anomalous growth of the local moments with increasing temperature can be understood from the observed large thermal expansion of the $c$-axis lattice parameter combined with strong magnetoelastic coupling. These effects originate from the strong tendency to form As-As dimers across the Ca layer in the CaFe$_{2}$As$_{2}$ family of materials. Our results emphasize the dual local-itinerant character of magnetism in Fe pnictides.

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We point out that all current Josephson-junction experiments probing directly the symmetry of the superconducting state in YBa2Cu3O7, can be interpreted in terms of the bilayer antiferromagnetic spin fluctuation model, which renders the superconducting state with the order parameters of extended $s$ symmetry, but with the opposite signs in the bonding and antibonding Cu-O plane bands. The essential part of our interpretation includes the Cu-O chain band which would have the order parameter of the same sign as antibonding plane band. We show that in this case net Josephson currents along and perpendicular to the chains have the phase shift equal to pi.

Absolute electronic Raman-continuum cross sections have been measured for orthorhombic single-domain Y-123 and Bi-2212 crystals and a tetragonal Tl-2223 film on a MgO substrate (${\mathit{T}}_{\mathit{c}}$=120 K) in different polarization geometries. They agree well with effective mass fluctuations obtained for Y-123 from Fermi-surface averages of the dispersion calculated from the full-potential linear muffin-tin orbital band structure of Andersen et al. The results suggest that anisotropic mass density fluctuations involving various sheets and regions of the Fermi surface are indeed responsible for the electronic Raman continuum and predictable with realistic local-density-approximation band-structure calculations. Decomposition into contributions from the four sheets of the Fermi surface permits separation of interband and intraband mass fluctuations. Anisotropies corresponding to the orthorhombicity and the purely tetragonal ${\mathit{A}}_{1\mathit{g}}$, ${\mathit{B}}_{1\mathit{g}}$, and ${\mathit{B}}_{2\mathit{g}}$ symmetries are determined for the three superconductors.

We report local density approximation plus Hubbard parameter $U$ calculations of the electronic structure of $A{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ ($A=\mathrm{Y},\phantom{\rule{0ex}{0ex}}\mathrm{P}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{N}\mathrm{d}$) including Coulomb correlations in the $f$ shell. For $A=\mathrm{Pr}$ (but not for $A=\mathrm{Nd}$) an additional band crosses the Fermi level, grabbing holes from the (super)conducting $\mathrm{pd}\ensuremath{\sigma}$ band. On doping Y or Nd with Pr the position of the hole-depleting band depends on the atomic number of the host rare earth, through the position of its $f$ level. This makes ${T}_{c}$ suppression in doped compounds different for different hosts the stronger the smaller the atomic number of the host is, and also explains why an external pressure reduces ${T}_{c}$ in doped compounds, opposite to the effect of the "chemical pressure" (substituting one rare earth by another with a smaller size).

We have studied the magnetic moments and magnetic anisotropy energy (MAE) of YCo5 and SmCo5 using full-potential linear augmented plane wave (LAPW) electronic structure calculations. Most previous calculations of the MAE for YCo5, using local density approximation (LDA) for the exchange-correlation potential, have found values significantly smaller (∼0.6 meV/f.u.) than experiment (∼3.8 meV/f.u.). The rest of the MAE is attributed to many body corrections. Our LAPW calculations using the generalized gradient approximation (GGA) instead of LDA and including nonspherical corrections give values ∼1.5 meV/f.u. The Co magnetic moment of YCo5−xCux, unlike the prediction of the virtual crystal approximation, decreases slowly with impurity concentration until dropping suddenly to zero at a critical dopant concentration. Correlation effects were found to be crucial for the MAE in SmCo5. While GGA calculations give MAE for SmCo5 of the wrong sign, including the LDA+U, correction brings it to ∼21 meV/f.u., in good agreement with the experimental value of 13–16 meV/f.u.

We report frozen-phonon local-density calculations for YBa2Cu3O7 of the infrared- and Raman-active apical-oxygen phonons in the c-direction. No sign of the suggested bistability or anharmonicity is found.

We suggest a microscopic model that provides a consistent explanation of the recent femtosecond pump-probe experiments on YBa[sub 2]Cu[sub 3]O[sub 7], including the fact that the reflectivity change in the superconducting state is much larger than that in the normal state. In this model, not only the oscillatory part of the reflectivity, but also the total reflectivity change, is due to displacive excitation of coherent phonons. The microscopic reason for this excitation is that superconductivity induces small displacements in the equilibrium positions of the ions, since the pairing energy depends on the density of states at the Fermi level, which changes with the ionic positions. When superconductivity is destroyed by the femtosecond laser pulse, the ions are pulled back to their normal equilibrium positions, thus exciting coherent phonons. The relative size of the oscillatory contribution to the reflectivity depends upon the ratio of the phonon period to the time scale of the pair breaking, and when this ratio is small, the oscillations are suppressed, as observed in the experiment. [ital Ab] [ital initio] caluclations confirm this model. The model also provides an explanation for why the mangitude of the 150 cm[sup [minus]1] mode below [ital T][sub [ital c]] may bemore » smaller than that of the 120 cm[sup [minus]1] mode.« less

We report inelastic neutron scattering measurements on Na2IrO3, a candidate for the Kitaev spin model on the honeycomb lattice. We observe spin-wave excitations below 5 meV with a dispersion that can be accounted for by including substantial further-neighbor exchanges that stabilize zigzag magnetic order. The onset of long-range magnetic order below T(N)=15.3 K is confirmed via the observation of oscillations in zero-field muon-spin rotation experiments. Combining single-crystal diffraction and density functional calculations we propose a revised crystal structure model with significant departures from the ideal 90° Ir-O-Ir bonds required for dominant Kitaev exchange.

A newly discovered family of the Fe-based superconductors is isostructural with the so-called 122 family of Fe pnictides, but has a qualitatively different doping state. Early experiments indicate that superconductivity is nodeless, yet prerequisites for the $s_\pm$ nodeless state (generally believed to be realized in Fe superconductors) are missing. It is tempting to assign a $d-$ wave symmetry to the new materials, and it does seem at first glance that such a state may be nodeless. Yet a more careful analysis shows that it is not possible, given the particular 122 crystallography, and that the possible choice of admissible symmetries is severly limited: it is either a conventional single-sign $s_{+}$ state, or another $s_\pm$ state, different from the one believed to be present in other Fe-based superconductors.

BiOCuS is a band insulator that becomes metallic upon hole doping. Superconductivity was recently reported in doped BiOCu$_{1-x}$S and attributed to spin fluctuations as a pairing mechanism. Based on first principles calculations of the electron-phonon coupling, we argue that the latter is very strong in this material, and probably drives superconductivity, which is however strongly depressed by the proximity to magnetism. We find however that BiOCu$_{1-x}$S is a quite unique compound where both a conventional phonon-driven and an unconventional triplet superconductivity are possible, and compete with each other. We argue that, in this material, it should be possible to switch from conventional to unconventional superconductivity by varying such parameters as doping or pressure.

A first-principles prediction of the q dependence of the electronic susceptibility of YBa2Cu3O7 and the relation to experimentally observed phonon anomalies is presented.

By analysis of the electronic contribution to the binding in A 3 C 60 , we show that the problem of orientational ordering can be mapped onto the fcc nearest-neighbor antiferromagnetic Ising model with J at the order of 100 K. For T

Using previously reported first-principle frozen-phonon LDA calculations we have calculated the effective superconducting and transport electron-phonon coupling constants. We have taken into account the anisotropy due to the difference between four bands crossing the Fermi level in YBa2Cu3O7, and found that because the anisotropy influence both electron-phonon coupling constants, but in the opposite direction, the superconducting constant becomes larger than the transport one. The absolute values of the effective coupling constants is close to 2. The superconducting gaps for the different bands vary by nearly an order of magnitude. We also discuss how various experiments might have been explained in terms of the interband anisotropy.

Various experiments indicate that ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$ are in the strong-coupling regime. There is also both theoretical and experimental evidence for a large coupling of high-frequency intramolecular phonons with the electrons. If only these phonons are relevant, it is difficult to explain the relatively low ${\mathit{T}}_{\mathit{c}}$. This paradox can be resolved by introducing additional coupling with the low-lying intermolecular modes. Such a model also provides a consistent explanation of the tunneling experiments, and of the non-BCS behavior of the critical fields, penetration depth, and NMR relaxation time.

Triangular-layered NiGa2S4, contrary to intuitive expectation, does not form a noncollinear antiferromagnetic structure, as do isoelectronic NaCrO2 and LiCrO2. Instead, the local magnetic moments remain disordered down to the lowest measured temperature. To get more insight into this phenomenon, we have performed first principles calculations of the first, second end third neighbors exchange interactions, and found that the second neighbor exchange is negligible, while the first and the third neighbor exchanges are comparable and antiferromagnetic. Both are rapidly suppressed by the on-site Hubbard repulsion.

Based on a numerically highly accurate local-density-approximation (LDA) calculation, we present a k\ensuremath{\cdot}p analysis of the interband optical absorption in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ in the infrared region (\ensuremath{\Elzxh}\ensuremath{\omega}0.1 eV). It is shown that the LDA band structure gives rise to three infrared interband transitions: A sharp peak for the in-plane (E\ensuremath{\perp}c) polarization at about 320 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, a wide maximum for E\ensuremath{\parallel}c at about 420 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and a structureless absorption (${\mathrm{\ensuremath{\epsilon}}}_{2}$\ensuremath{\approxeq}const) for E\ensuremath{\parallel}c. The first feature is due to transitions between the apical-oxygen-derived bands, the second one to that between the z-even and z-odd ${\mathrm{CuO}}_{2}$ plane bands, and the third one to the transitions between the chain band and the z-odd plane band. The possibility of observing these features in experiment is discussed.

ac susceptibility measurements of superconducting ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ powders in magnetic fields to 30 T yield a roughly linear ${\mathit{H}}_{\mathit{c}2}$(T) curve extending up to the highest experimental fields. Samples prepared by two different methods give -${\mathit{dH}}_{\mathit{c}2}$/dT=2.14\ifmmode\pm\else\textpm\fi{}0.08 T/K, with ${\mathit{T}}_{\mathit{c}}$=18.7 K. The observed ${\mathit{H}}_{\mathit{c}2}$ at low temperatures exceeds the ${\mathit{H}}_{\mathit{c}2}$(T) curve from the standard theory by Werthamer-Helfand-Hohenberg. We discuss the role of flux motion and evidence for enhancement of ${\mathit{H}}_{\mathit{c}2}$ by intrinsic mechanisms such as strong coupling, Fermi surface anisotropy, and/or granularity of the samples.

We present evidence for the existence of two close-lying, nearly parallel energy bands in the vicinity of the Fermi level in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. The electrons in these bands are located in the Ba-O planes and have nearly no Cu-O chain or plane components. The higher band is partially unoccupied and the corresponding Fermi surface was recently measured by the de Haas\char21{}van Alphen effect. We have calculated the extremal Fermi-surface areas and the results are in excellent agreement with experiment, when spin splitting in high magnetic field is taken into account. We show furthermore that interband transitions for in-plane polarizations are allowed between these two bands and that they result in a sharp peak at about 350 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in our calculated optical conductivity.

The electronic part \ensuremath{\eta} (the Hopfield factor) of the electron-phonon coupling constant \ensuremath{\lambda} for alkali-metal-doped fullerenes ${\mathit{A}}_{3}$${\mathrm{C}}_{60}$ is calculated within the rigid muffin-tin-potential approximation. It is found that \ensuremath{\eta} is large for tangential atomic motions, while for the radial vibrations \ensuremath{\eta} is 20 times smaller. We have calculated \ensuremath{\eta} for three lattice constants (a=14.1, 14.4, and 14.6 \AA{}) corresponding approximately to those of ${\mathrm{C}}_{60}$, ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$, and (hypothetical) ${\mathrm{Cs}}_{3}$${\mathrm{C}}_{60}$, and found \ensuremath{\eta}=21, 32, and 36 eV/A${\mathrm{\r{}}}^{2}$. Using semiempirical nearest-neighbor force constants we estimated \ensuremath{\lambda}=0.49, 0.77, and 0.83, and 〈${\mathrm{\ensuremath{\omega}}}_{\mathrm{log}}$〉=870 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for the average phonon frequency. The McMillan formula yields ${\mathit{T}}_{\mathit{c}}$=5, 36, and 44 K for these lattice constants, in reasonable agreement with the available experimental data. The relatively high-temperature superconductivity in ${\mathit{A}}_{3}$${\mathrm{C}}_{60}$, as well as the strong dependence of ${\mathit{T}}_{\mathit{c}}$ on the dopant, is fully explained within the framework of the conventional superconductivity theory.

We have calculated the renormalization of the specific heat in the normal state and the specific heat jump at Tc, using a realistic Eliashberg function, extracted from tunneling spectroscopy. The magnitude of the Eliashberg function was scaled so as to have the total coupling constant λ from 1.5 to 2.5. Using these calculations, we have analyzed recent measurements of the specific heat and have found that they can be reconciled with the band structure calculations, if λ≈2.

The FexCo1−xS2 system is predicted, on the basis of density functional calculations, to be a half metal for a wide concentration range. Unlike most known half metals, the half metalicity in this system is expected to be very stable with respect to crystallographic disorder and other types of defects.

Using the local-density approximation and the full-potential linear muffin-tin-orbital method we have calculated the total energy of ${\mathrm{Ba}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{K}}_{\mathit{x}}$${\mathrm{BiO}}_{3}$ for x=0 and 0.5 as a function of tilting and breathing distortions. For x=0 we find an instability for a combination of both distortions and we correctly reproduce the monoclinic structure. For x=0.5 we correctly find the cubic phase to be stable. The frequencies of the tilting and breathinglike phonons are calculated for x=0 and 0.5. In the cubic structure we calculate the strength ${\ensuremath{\lambda}}_{\mathit{b}}$ of the electron-phonon coupling for the breathing mode as a function of x using a rigid-band approximation. For 0.37x0.5, ${\ensuremath{\lambda}}_{\mathit{b}}$\ensuremath{\approxeq}0.3 and follows the trend of ${\mathit{T}}_{\mathit{c}}$. The superconductivity is conceivably mediated by the electron-phonon coupling.

We have measured and calculated the dependence of the Raman phonon intensities of YBa{sub 2}Cu{sub 3}O{sub 7} on laser frequency. The local-density approximation and the linear muffin-tin-orbital method were used for the calculations. We find good agreement not only in the absolute phonon intensities in {ital zz} or {ital xx}/{ital yy} polarization but also in the shape of the resonance profiles. These results indicate that the local-density approximation gives an essentially correct description of the band structure and of the electron-phonon interaction {plus minus}2 eV around the Fermi energy. We interpret our data in terms of specific interband transitions and estimate the mode mixing.

{ital Ab} {ital initio} frozen-phonon calculations were performed for YBa{sub 2}Cu{sub 3}O{sub 7} for the five {ital A}{sub {ital g}} Raman-active and for two {ital B}{sub 1{ital u}} infrared-active optical {bold q}={bold 0} modes, with use of the local-density approximation and the full-potential linear-muffin-tin-orbital method. The full {ital A}{sub {ital g}} dynamical matrix was calculated using 98 {bold k} points in the 1/8 Brillouin zone. The theoretical and experimental equilibrium structures and phonon frequencies {omega}{sub {nu}} agree well. Phonon linewidths {gamma}{sub {nu}{bold q}}, due to electronic intraband transitions in the normal state, and electron-phonon coupling constants {lambda}{sub {nu}{bold q}}{identical to}{gamma}{sub {nu}{bold q}}/({pi}{ital N}(0){omega}{sub {nu}}{sup 2}) were calculated for the {ital A}{sub {ital g}} modes and small, transverse {bold q}. We estimate that {lambda}{approx}1 for the sum over all modes. The phonon shifts and broadenings observed for {ital T}{lt}{Tc} by Raman scattering are well accounted for by conventional strong-coupling theory and our calculated electron-phonon coupling.

The Hopfield factor (electronic part of the electron-phonon coupling constant) is calculated in the rigid-muffin-tin approximation (RMTA) for several perovskite high-{Tc} superconductors. Calculations were performed in the conventional spherical'' approximation and take into account the proper local symmetry. It is shown that the layered perovskite crystal symmetry generally favors strong electron-phonon interaction on the copper sites. We also estimate some non-RMTA effects.